“I could see the suspects taking cover behind their black Mercedes,” Kitzenberg told WBZ-TV. “I originally thought it was related to the MIT shooting but when I started taking pictures and witnessing it and I saw the explosives, I knew we were dealing with something bigger.”

The Tsarnaev brothers taking aim and firing on the officers. The red circle highlights the pressure cooker bomb that was used just moments after this photo was taken. (Photo courtesy: Andrew Kitzenberg)

In the photos, the two men are seen with what police later confirmed, was a pressure cooker bomb.

“From my vantage point, I could see very clearly a small metal device that resembled the pressure cooker bombs from images I’d seen earlier that week,” he said. “I saw them throwing explosives toward officers down our street.”

Kitzenberg also captured Tamerlan Tsarnaev on the ground as his brother Dzhokhar drove toward police.

Dzhokhar Tsarnaev ran over his brother as he drove away from the scene. Tamerlan Tsarnaev later died.

Police spent all day Friday searching for Dzhokhar in a manhunt that locked down the city of Watertown and surrounding communities.

“I witnessed him (Tamerlan Tsarnaev) running down the street, shooting at officers before he was ultimately taken down just before he reached officers,” Kitzenberg said.

Kitzenberg is a Babson College graduate and owner of onHand, a company that makes USB drive wristbands.